Tarshish is a city referred to about a dozen times in the Bible and has been widely accepted as another version of Tartessos. Josephus, the Jewish historian who wrote during the 1st century AD, was confident that it referred to Tarsus in Cilicia, Turkey, the birthplace of St. Paul. The Septuagint Bible uses Karkendonos where it refers to Tarshish in Isaiah 23:1, which was the Greek form of the name for North African Carthage. This could imply that the founders of Carthage and Tarsus were the same. We know that Carthage was founded by Tyrians and we also know that Cilix, a Tyrian, gave his name to Cilicia when he settled it. Andis Kaulins has claimed that Carthage was possibly built on the remains of Tartessos (i)!
Immanuel Velikovsky was of the opinion that “Tarshish was the name employed by the writers of the Old Testament to designate Crete as a whole, or its chief city Knossos.” as explained in a paper by his former associate Jan Sammer(m).
In 2008, Rainer Kühne published a paper titled Tartessos-Tarshish was the model for Plato’s Atlantis in which he identifies Tartessos as Tharshish, locates it in the Donana Marshes of southern Spain and suggests that it lasted from the tenth to the sixth centuries BC(p).
Utica was a Phoenician port city on the northern coast of what is now Tunisia. It no longer exists and its site is now some miles inland because of silting. It is also one of a number of suggested locations for Tarshish(f).
Tarshish/Tartessos is thought by many others to be alternative names for Atlantis. There is a consensus that it was a coastal city in Southern Spain, near modern Cadiz. Despite the efforts of many, its location is still unknown, which can probably be explained by the fact that the coastline has altered considerably over time. Adolf Schulten, who was convinced that Tartessos was Atlantis, spent many years searching, unsuccessfully, for Tarshish in Andalusia. Louis Millette is a modern writer who supports this identification but has offered little by way of evidence.
In 1927, Edwin Björkman devoted a third of his book, Search for Atlantis  to a discussion of Tarshish and its possible connection with Atlantis.
Other locations have been suggested, such as Tharros in Sardinia, Troy and even Malta where Tarxien may be considered an echo of Tarshish. Tharros sometimes referred to as a ‘second Carthage’ had its port located as recently as 2008(d). The suggestion that Tharros was Tarshish was based on their similar-sounding names and the reference to Tarshish in the Phoenician inscription on the ‘Nora Stone’ discovered at Nora on the south coast of Sardinia in 1773.
The Brit-Am organisation, which seeks to identify the ten lost tribes of Israel has published an extensive series of papers about Tarshish(n). Responding to a question about Atlantis and Tarshish they wrote – “Atlantis does seem to have existed and does appear to have been somewhere in the Atlantic coastal area. Tarshish is a good candidate or at the least would have had some contact with Atlantis.”(o)
Quite a variety of locations have been offered as the site of Tarshish(f)(k).
Aaron Arrowsmith (1750-1832), a British cartographer and geographer was of the view that “Tartessus was a territory established by adventurous traders who settled in the Iberian peninsula after moving from the ancient city of Tarsus in Asia Minor (modern Turkey).” 
It is accepted that biblical silver was sourced from ‘Tarshish’, initially assumed to be Tartessos in Spain. Recent studies employing lead isotope tests, when applied to Phoenician silver hoards(g) revealed that both Spain and Sardinia were possible sources. However, it might be argued that the Nora Stone may give Sardinia a somewhat stronger claim.
A more radical idea was put forward in 2012 by the Spanish researcher, José Angel Hernández, who proposed that the Tarshish of the Bible was to be found in the coastal region of the Indus Valley and that Tartessos was a colony of the Indus city of Lhotal and had been situated on both sides of the Strait of Gibraltar!(a)(b) This view is apparently supported by biblical references (1 Kings 9:26, 22:48; 2 Chr. 9:21) that note that the ‘ships of Tarshish’ sailed from Ezion-Geber on the Red Sea’s Gulf of Aqaba!
Jim Allen, who has been the leading supporter for decades of the idea of Atlantis being situated in the northern Andes, has also proposed that Tarshish had been a South American city. “The more probable site of Tarshish however lies on an island at the entrance to the Pilcomayo River opposite Asuncion, since satellite photos show that at this point the Pilcomayo forks into two arms exactly as per the ancient text, creating an island between the arms of the river. Moreover also in accordance with the ancient text, the river discharges into a broad bay – the Bay of Asuncion and this part of the Paraguay River also comprises shallows and sandbanks.”(l) This demonstrates that Allen saw Atlantis and Tarshish as separate entities.
However, if Tarshish was another name for Atlantis and according to the bible it existed at the time of Solomon, circa 1000 BC, we are confronted with a contradiction of Plato’s 9,000 years elapsing since the destruction of Atlantis and the visit of Solon to Sais. King Jehoshaphat reigned around 860 BC and planned to send a fleet to Tarshish, just 200 years before Solon, so the likelihood of Tarshish being Atlantis is a rather remote possibility.
A recent suggestion by a Dutch commentator, Leon Elshout, places the biblical Tarshish in Britain(h) an idea supported by a Christadelphian website(j).
(i) Pillars of Heracles – Alternative Location (archive.org)
(o) Scroll down to Question 2 in (n) *